Pest of the Week: the BAGWORM

Well now, here’s a new yucky one for ya! The other day, I looked out on the big flowerpot where two random sunflowers appeared this summer, and I saw a… well… a thing…. crawling. It looked like something out of a horror movie. I snapped a photo and posted it online, and by the miracles and graces of Social Media was able to get an ID. The ID came from a friend, Chazz, who studied Plant Protection and Pest Management at UC Davis – how’s that for credentials?

This pest overwinters as eggs inside the female’s abdomen inside the bag she constructed. Females lay 500-1000 eggs in each bag during the previous fall. Eggs start hatching from late May through early June. Upon hatching, young larvae crawl out of the bag and start to feed and construct silken shelters over their bodies. As the larvae (Image 1) grow over the eight to ten week feeding period, they continue to enlarge the exterior of their bags with pieces of foliage, bits of bark, or other plant parts. Feeding and development usually continue until August. Mature larvae loop strands of silk around a twig and become firmly attached. After the top of the bag is closed, larvae reverse their position in the bags so that their heads face downward. They then change into the pupal (resting) stage and remain in this life stage for about 4 weeks. During September and early October the males (Image 2) leave their cases and fly to bags containing females where mating takes place. Each mated female deposits a mass of eggs inside her bag. She crawls out of the bag after laying eggs, drops to the ground and dies. This pest species spends the winter inside the bag until the following spring.

I have noticed that there are more dangling from the tree, and notice the resident Song Sparrows have also been feasting on them.

While it is my neighbor’s tree, it is her decision, but the dilemma is spray with chemicals (which is the most effective method) or leave it untreated and risk infestation?